The sendto() call in walk_tx() was passing NULL as the buffer argument,
which can trigger a -Wnonnull warning with some compilers.

Although the size is 0 and no data is actually sent, passing a null
pointer is technically incorrect.

This commit changes NULL to an empty string literal ("") to satisfy the
non-null argument requirement and fix the compiler warning.

Signed-off-by: Wake Liu <wakel@google.com>
---
 tools/testing/selftests/net/psock_tpacket.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/net/psock_tpacket.c b/tools/testing/selftests/net/psock_tpacket.c
index 221270cee3ea..0c24adbb292e 100644
--- a/tools/testing/selftests/net/psock_tpacket.c
+++ b/tools/testing/selftests/net/psock_tpacket.c
@@ -470,7 +470,7 @@ static void walk_tx(int sock, struct ring *ring)
 
 	bug_on(total_packets != 0);
 
-	ret = sendto(sock, NULL, 0, 0, NULL, 0);
+	ret = sendto(sock, "", 0, 0, NULL, 0);
 	if (ret == -1) {
 		perror("sendto");
 		exit(1);
-- 
2.51.0.534.gc79095c0ca-goog